1. Field of the Invention
The invention relates to a communication device that communicates between an independent center and a user's home by making use of the idle time on a telephone network which connects the switching system of the local telephone exchange and the telephone in said user's home.
2. Description of the Prior Art
Telephone communication normally involves the connection of the switching system of a telephone exchange and a user's telephone through the medium of a telephone network. When the telephone receiver is lifted off the hook, a loop is formed with between the telephone and the exchange's switching system by way of the telephone network and voice communication is made possible by the transmission of signals around said loop.
There are known communication devices which make use of a network's idle time for the unidirectional transmission of broadcast data in the form of, for example, music data to the user's home. This type of communication device calls for the installation in a telephone exchange of an exchange device which is used to switch the telephone network selectively between the switching system of the exchange itself and a facility installed in an independent center for the transmission of analog data in the form of speech or music. Each user's home is fitted with a home device with a speaker, which is connected to the telephone network and which, when the receiver is lifted off the hook, connects the exchange device to the exchange's switching system itself to enable voice communication and, when the receiver is placed on the hook, switches the exchange device to said independent center From which broadcast data is transmitted by way of the telephone network to users' home devices. In practice, a plurality of center units are normally connected to a single exchange device which can be turned on and off or switched selectively between said center units (to select different broadcast data channels) by the remote operation of the user' home devices.
However, a communication device, which makes use of idle time in this way, enables unidirectional one-to-many communication only from a center unit to a plurality of home devices. Home devices, on the other hand, have been confined to the remote switching of the exchange device on and off and the remote selection of center units. It has not, however, been possible for data to be channeled to a specific user from a center nor for a specific user to transmit information in data form to a center. It has thus been impossible, for example, either to
(a) transmit data from a center to a specified user and to confirm the due arrival of said data by the return of data from said user to said center, or to PA1 (b) transmit requests for specific pieces of music or instructions in data form from a user's home to a center, or to PA1 (c) create a protocol to enable error-free transmission up and down between centers and users.